1. Field of the Invention
The present invention relates to a method for noise reduction in the operation of a gradient coil of a magnetic resonance apparatus, wherein at least a portion of the gradient coil is in contact with a reaction resin molding material.
2. Description of the Prior Art
In diagnostic magnetic resonance tomography apparatuses, considerable disturbing noise arises due to structural oscillations which occur due to the operation of the apparatus with controlled gradient coils. The noise level can exceed 120 dB.
For noise reduction, both passive and active measures are used. One passive noise reduction technique is to increase the rigidity of the gradient coil, as is known from German OS 41 41 514. The intrinsic oscillation behavior of the gradient coil system is thereby matched to smaller oscillation amplitudes and to higher frequencies, so that an effective damping can then be achieved using sound insulation measures.
German OS 41 41 514, as a further passive measure for reduction of disturbing noise, discloses connecting a casting resin molding compound with the gradient coils, which compound also achieves a good sound damping at the operating temperature of the gradient coil system, in addition to having a high modulus of elasticity. Due to the intensive cross-linking among one another of the macromolecules of the resin, a duroplast molding material can never simultaneously exhibit a high modulus of elasticity and a good inner mechanical damping.
As a further passive measure for noise reduction, it is known to build a hole structure into the gradient coil.
In European Application 0 507 528, an active measure for noise reduction is described employing the production of counter-sound via loudspeakers. In this way, noise at the ear of the patient is reduced.
A further measure for noise reduction in gradient coils is disclosed in U.S. Pat. No 4,954,781, which teaches arranging a sandwich structure between the patient to be examined and the main magnet. The sandwich structure includes a visco-elastic layer pressed by two parts.
The Derwent abstract for Japanese Application 08-231731 discloses polymer parts as an additive for resin compositions that include of a polymer core element and a polymer shell element, which respectively have specific glass transition temperatures. As an additive to resin compositions, an improved and effective suppression of oscillations is achieved over a broad temperature range.
The Derwent abstract for Japanese Application discloses 02-169637 a damping material for cars, machines, etc., employing a resin with a specific glass transition temperature. The glass transition temperature is in the range from 0.degree. C. to 60.degree. C.